Integrated nitrogen removal with intermediate feed gas separation in the production of liquefied natural gas

Integrated nitrogen removal with intermediate feed gas separation in the production of liquefied natural gas

  • CN 105,043,011 B
  • Filed: 04/24/2015
  • Issued: 07/31/2020
  • Est. Priority Date: 04/24/2014
  • Status: Active Grant
First Claim
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1. A method for producing a denitrified liquefied natural gas product, the method comprising:

  • (a) Introducing a natural gas feed stream into the warm end of a main heat exchanger, cooling and at least partially liquefying the natural gas feed stream with a refrigerant circulating in a closed loop refrigeration system, and withdrawing a cooled and at least partially liquefied stream from an intermediate location of the main heat exchanger;

    (b) Expanding, partially vaporizing and separating the cooled and at least partially liquefied stream to form a nitrogen-rich natural gas vapor stream and a denitrogenated natural gas liquid stream;

    (c) Withdrawing a portion of the nitrogen-enriched natural gas vapor stream to form a stripping gas stream;

    (d) Separately reintroducing the remaining part of the nitrogen-rich natural gas vapor stream and the denitrogenated natural gas liquid stream into an intermediate location of the main heat exchanger to further cool the remaining part of the nitrogen-rich natural gas vapor stream and the denitrogenated natural gas liquid stream in parallel within the same heat exchanger with refrigerant circulating in the closed loop refrigeration system of step (a), the remaining part of the nitrogen-rich natural gas vapor stream being further cooled and at least partially liquefied to form a first at least partially liquefied nitrogen-rich natural gas stream and the denitrogenated natural gas liquid stream being further cooled to form a first liquefied natural gas stream and the first at least partially liquefied nitrogen-rich natural gas stream being withdrawn from the cold end of the main heat exchanger;

    (e) Expanding and partially vaporizing the first at least partially liquefied nitrogen-rich natural gas stream, introducing the expanded and partially vaporized stream into a distillation column to separate the expanded and partially vaporized stream to form a nitrogen-rich vapor product and a second liquefied natural gas stream;

    (f) Introducing the stripping gas stream into the bottom of the distillation column;

    (g) Expanding, partially vaporizing and separating the second liquefied natural gas stream to form a denitrogenated liquefied natural gas product and a nitrogen-rich natural gas vapor;

    (h) Withdrawing at least a portion of the nitrogen-enriched natural gas vapor as a recycle stream;

    (i) Compressing the recycle stream to form a compressed recycle stream; and

    (j) Returning the compressed recycle stream to the main heat exchanger to be cooled and at least partially liquefied together with the natural gas feed stream;

    Wherein refrigeration in the main heat exchanger is provided by the closed loop refrigeration system, refrigerant circulated by the closed loop refrigeration system passing through the main heat exchanger and warming in the main heat exchanger;

    Wherein a portion of the nitrogen-rich vapor product formed in the distillation column is condensed by a condenser heat exchanger to form a condensed nitrogen-rich vapor product that is introduced into the top of the distillation column to provide reflux; and

    Wherein a portion of the refrigerant exits from the cold end of the main heat exchanger and expands to form cold refrigerant that is introduced into the condenser heat exchanger to provide condensation and then enters the middle section of the main heat exchanger.

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